Question

I have an array of Place objects. Each Place object has a name and code property, both strings. Each Place object already has a code, but I need to look up the name property from a server. I get back 2 arrays: one contains name, the other codes. These arrays are ordered so that the name at some index in the nameArray corresponds exactly with the code at the same index of the codeArray.

I have been looping through the array of Place objects, then checking to see if the code property for that Place is the same as the current index in the codeArray. If it is, I set the name of that Place by using the same index in the nameArray:

for(int i = 0; i < [placesArray count]; i++)
{
    for(int j = 0; j < [codeArray count]; j++) {

       if([[[placesArray objectAtIndex:i] code] isEqualToString:[codeArray objectAtIndex:j]]) {   
            [[placesArray objectAtIndex:i] setName:[nameArray objectAtIndex:j]];
       }
    }
}

This works but isn’t terribly fast – it can take 30 seconds with 1000+ Places to loop through.

Is there a faster way?

Answer 1

As with anytime you’re trying to optimize performance, you should profile the code using Instruments to find out where the bottleneck actually is. That said, looping through the placesArray for each name in the nameArray and doing a string comparison is pretty inefficient.

How about something like this?

NSMutableDictionary *placesByCode = [NSMutableDictionary dictionaryWithCapacity:[placesArray count]];
for (Place *aPlace in placesArray) {
    [dictionary setObject:aPlace forKey:aPlace.code];
}

NSMutableDictionary *namesByCode = [NSMutableDictionary dictionaryWithCapacity:[namesArray count]];
for (int i=0; i<[namesArray count]; i++) {
    NSString *name = [namesArray objectAtIndex:i];
    NSString *code = [codeArray objectAtIndex:i];
    [namesByCode setObject:name forKey:code];
}

for (NSString *code in namesByCode) {
    Place *place = [placesByCode objectForKey:code];
    place.name = [namesByCode objectForKey:namesByCode];
}

Looking up each place by its code in the dictionary should be quite a bit faster than manually looping through the whole place array for each name.